There are many historical and emerging arguments against patent systems. For one, patents can be quite obstructive and create gridlock. Michael Heller calls this effect the “anti-commons”: too many people have too many rights. An “anti-commons” prevents the holders of these rights from assembling them, which decreases social-welfare. His most contemporarily relevant example is in biotechnology. To develop new drugs, companies often require the license of patents that belong to other companies. However, as more and more licenses are required, the bargaining and transaction costs may become excessive and outweigh the future financial expected value of a marketable drug. Here, Heller argues, the patent system works backwards and consequently produces the opposite goal of what it is designed to do: increase social welfare. Accordingly, the latest and greatest Viagra may be stuck in the labs because the costs of developing it are too prohibitive.

You could talk about the (recent) impossibility of bringing to market a second test for breast cancer, because patents on the BRCA-1 and 2 genes prevented it. The ACLU and PubPat? overturned the patent in court, but that solution was not so much an overcoming of a patent thicket as an elimination of the patent itself.